1. Field of the Invention
The present invention relates to the enhancement of discharge properties and endurance of lead-acid battery.
2. Description of the Related Art
A lead-acid battery has been widely applied as an inexpensive reliable high safety secondary battery for SLI (Starting, Lighting and Ignition) and other purposes. However, a lead-acid battery has a low specific energy that gives a serious obstacle to the development of its application to EV (electric vehicle), etc.
Many methods have long been studied to enhance the specific energy of lead-acid battery. One of these proposed methods is to add tin in the positive active material to enhance the discharge properties of the lead-acid battery. However, this approach is disadvantageous in that tin thus added is eluted from the positive active material with the electrolyte and then deposited on the negative plate to lower the hydrogen overvoltage of the negative plate and hence cause much lead sulfate to be accumulated on the negative plate, thereby reducing the endurance of the lead-acid battery.
It is an object of the present invention to enhance the specific energy of a lead-acid battery by adding tin into a positive active material as well as to prevent the reduction of endurance of a lead-acid battery by inhibiting the deposition of tin on the negative plate.
In a lead-acid battery according to the present invention, a positive acid material includes tin in an amount of from not less than 0.2% to not more than 5% based on the weight thereof. The density of the positive active material after formation is from not less than 3.75 g/cc to not more than 5.0 g/cc. When the lead-acid battery is produced by a battery container formation, a time required between the injection of an electrolyte and the beginning of battery container formation is from not less than 0.1 hours to not more than 3 hours.
According to the present invention, it is possible to remarkably improve the discharge properties and endurance of lead-acid batteries.